Viewing systems are important to the proper operation of motor vehicles. Such systems must be capable of operating in a wide range of inter-scene brightness ranging from strong sunlight to moonlight. They must also perform well in a wide range of intra-scene brightness as may occur from viewing a nighttime scene containing car headlights. Still further, frame rates must be attainable so that the displayed view appears to be real-time.
Traditionally, vehicle viewing systems have used a plurality of mirrors to allow the operator to see objects behind and beside the vehicle. The use of mirrors has resulted in several difficulties, including blind spots due to opaque body structures, distortion due to convexity, inability to modify color balance for night vision, and wind resistance due to outside mounting.
Another difficulty with current vehicle viewing systems is an inability to properly display the intensity of a dimly lit scene. The human eye is much more sensitive to light when adapted to dimly lighted street and highway driving at night than in the daytime. Viewing relatively bright images, such as a display screen with a relatively high intensity, causes changes in the retina which substantially and subtly reduce visual sensitivity to dimly lit scenes. Following exposure to brighter lights, this effect reduces the perception of and resulting reaction time to dimly lit scenes.
Still another difficulty with current vehicle viewing systems is the inability to alter the balance between a dim and bright portion of a scene. For example, headlamps of a trailing vehicle are frequently annoying to a driver. The brightness obscures visibility of much or all of other features in the rearward field of view, and may be bright enough to further mask visibility in portions of the forward field of view. Electrochromic mirrors have eliminated most of the annoyance glare without darkening excessively but cannot alter the balance between dim and bright portions of the same scene and cannot effectively amplify the intensity of a dimly lit scene.
Yet another difficulty with current vehicle viewing systems is the inability to shift the color balance of a displayed scene in response to changing ambient light conditions. In particular, blue light is more damaging to night vision than red light.
To reduce these problems and others, vehicle viewing systems employing cameras and displays have been proposed. Typically, one or more cameras are mounted on the sides, roof or rear of the vehicle. The video output may be processed to blend the views from multiple cameras, extract distance information, and adapt to changing environmental conditions. One or more displays are used to present the raw or processed video data to the operator.
Consequently, a need exists to produce a vehicle viewing system with extended dynamic range capable of operating effectively across wide intra-scene and inter-scene brightness levels. The system must also reduce the effects of display glare and not subject the vehicle operator to light levels and color balances that might compromise night vision.